Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND TOOL FOR FINE BLANKING OF WORKPIECES WITH SMALL
CORNER RADII AND GREATLY REDUCED DRAW-IN A ONE-STAGE
ARRANGEMENT
SCOPE OF THE INVENTION
[0001] The invention relates to a method for manufacturing
workpieces with small corner radii in relation to the thickness to be
cut, and greatly reduced edge reduction in a fine blanking tool of a
fine blanking machine, wherein the workpiece is clamped between two
tool parts respectively, consisting of an upper and a lower cutting
die as well as of an upper and a lower cutting punch, and the cutting
is realized by the combined efforts of upper and lower cutting
punches.
[0002] The invention further relates to a tool for fine blanking
of workpieces with small corner radii in relation to the thickness
to be cut, and greatly reduced edge reduction, from a cutting strip,
a sheet a coil material or the like with two clamping the latter
tool halves respectively consisting of at least one cutting die and
one cutting punch.
BACKGROUND OF THE INVENTION
[0003] The limitations of fine blanking of portions with small
corner radii in relation to the thickness of the sheet to be cut and
to the quality of the material are sufficiently known. Based on
experience, a fine blanking severity is defined which distinguishes
the severity degrees Si (easy), S2 (medium) and S3 (difficult) (see
KLOCKE, WZL/Fraunhofer IPT, "Blanking and Fineblanking", page 30).
Thus the severity degree is essentially defined by the cutting path
geometry and the thickness of the metal sheet. For this, the
cutting path geometry is divided into simple geometric basic areas
such as corner radii, hole diameters, groove and fin widths. From
the ratio between a geometric dimension and the
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thickness of the metal sheet, the severity degree of fine
blanking is defined, which grows with growing metal sheet
thickness. That means that fine blanking of large-area thin
parts is easier than fine blanking of narrow fins or rings
with greater sheet thickness. Also obtuse-angled corners with
big radii are to be cut better than sharp-cornered structures
with small radii.
[0004] A method is known from DE 39 31 320 Cl for
manufacturing burr-free workpieces by punch counter cutting,
for example, in an fine blanking tool, wherein a cutting strip
from which the workpiece is to be cut is clamped between two
tool parts, respectively consisting of an upper and a lower
cutting die as well as of an upper and a lower cutting punch.
The cutting is realized by the combined efforts of upper and
lower cutting punches, wherein cutting of the workpiece is
started along a cutting line and then cut out in the opposite
direction.
This state of the art exactly shows the intended
reduction on both sides as a result of counter cutting.
[0005] Typical characteristics of fine blanking parts are
edge reduction and burr. Especially at corner portions, edge
reduction occurs, which growing with corner radii becoming
smaller and with increasing sheet thickness. The reduction
depth may be around 20 % and the reduction width may be 30 % of
the sheet thickness or more (see DIN 3345, Feinschneiden, Aug.
1980). Thus, this reduction depends on the thickness and
quality of the material, so that controlling it is possible
only in a limited way, and often results in limited functioning
of parts, for example, because of the absence of sharp-edged
tips of interlocking parts, or because of changes in the
functional length of parts.
SUMMARY OF THE INVENTION
[0006] One aspect of the invention is to improve a method
and a tool for manufacturing workpieces in such a way that
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fine blanking can be also applied for parts with small corner
radii and sharp-edged corners with greater sheet thickness,
without limiting the function of the parts and at the same
time providing economic advantages.
[0007] This object is solved by a method and tool of the
kind mentioned herein.
[0008] Other advantageous aspects of the method and the
tool can be learned from the following description.
[0009] In accordance with one embodiment of the
invention, fine blanking becomes economically applicable for
portions of parts with small corner radii and sharp edge
portions, for example, interlocking parts with greater
thickness. One approach is based on the principle of
different cutting directions of the geometries of parts
converging without corner radius.
[0010] Thus the part to be cut consists of at least two
cutting geometries, for example, a circular geometry and a
toothed geometry, wherein the process of fine blanking is
executed in a one-stage arrangement. In a first partial step
an addendum circle structure of the interlocking part is cut
out of the cutting strip in a vertical working direction.
There follows the cutting out of the blank spaces between the
teeth in a working direction, opposite to the first partial
step.
[0011] One special advantage of the method according to the
present invention is that the converging tool geometries are
not pressure loaded at the same time, and not in the same
direction. The pressure loads in the corner area of the
workpieces thus can be significantly decreased, so that complex
part geometries also of greater thickness, can be fabricated by
fine blanking with sharp edges, massively reduced rollover and
precise functional length.
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[0012] Because of the specifically selected cutting geometry of
the first partial step, it is planned that the rollover is filled up
again during the second partial step.
[0013] The method and tool according to the present invention only
require a one-stage arrangement and further make it possible to
minimize the application of multi-step fabrication processes, whereby
the fine blanking process becomes more efficient in the case of
forming parts with complex structure and greater thickness.
[0013A] Accordingly, in one aspect the present invention
resides in a method for manufacturing a workpiece with relatively
small corner radii in relation to a thickness to be cut and
reduced edge reduction by fine blanking in a fine blanking tool of
a fine blanking machine, the method comprising:clamping the
workpiece between two tool parts respectively consisting of an
upper and a lower cutting die, as well as of an upper cutting
punch and a lower cutting punch, wherein cutting is realized by
combined efforts of said upper and lower cutting punches,shaping
the workpiece in a one-stage arrangement in at least two
chronologically successive cutting operations in different cutting
directions in a single stage, said at least two chronologically
successive cutting operations comprising the following partial
operations: (A) cutting out a semi-finished product corresponding
to the geometry of the workpiece in a first cutting process in
vertical working direction without significant rollover; and
(B)final cutting of the semi-finished product fabricated according
to operation (A) in at least one further cutting process in a
working direction opposite to that of operation (A), wherein the
rollover of the partial operation (A) at least in the corner area
is filled up again, each of the partial operations (A) and (B)
comprising cutting along uncommon cutting lines.
[00138] In another aspect, the present invention resides in a
tool for fine blanking of a workpiece with relatively small corner
radii in relation to a thickness to be cut and reduced edge
reduction from a cutting strip, a sheet of a coil material or
other suitable starting material, comprising: two tool halves
respectively including at least one cutting die and one cutting
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punch, the cutting punch being designed as a multi-part main punch
configured to shape a workpiece in a one-stage arrangement
comprising several partial operations so as to cut out a first
cutting geometry of a semi-finished product, at least one
5 allocated punch for a second, final cutting of the semi-finished
product acting in vertical working direction with respect to the
main punch, wherein the at least one allocated punch is arranged
with respect to the first cutting geometry in a way that said at
least one allocated punch can be applied to the semi-finished
product having regard to the first cutting geometry without
applying the pressure load in a same direction as the main punch,
each of the main punch and at least one allocated punch traversing
uncommon cutting lines throughout respective cutting of the semi-
finished product and final product.
[0013C] In another aspect the present invention resides in a
method for manufacturing a workpiece with relatively small corner
radii in relation to a thickness to be cut and reduced edge
reduction by fine blanking in a fine blanking tool of a fine
blanking machine, the method comprising: clamping the workpiece
between two tool parts respectively consisting of an upper and a
lower cutting die, as well as of an upper cutting punch and a
lower cutting punch, wherein cutting is realized by combined
efforts of said upper and lower cutting punches, shaping the
workpiece in a one-stage arrangement in the fine blanking machine
in at least two chronologically successive cutting operations in
different cutting directions in a single stage, said at least two
chronologically successive cutting operations comprising the
following partial operations: (A) with one of said upper and lower
punches, cutting out a semi-finished product corresponding to a
first geometry of the workpiece by cutting along a first cutting
line in a vertical working direction, said cutting resulting
substantially without rollover; and (B) with another of said upper
and lower punches, final cutting of the semi-finished product,
fabricated according to operation (A), to cut material from the
semi-finished product and thereby refine the first geometry, said
final cutting comprising cutting along a second cutting line
having a different geometry of cutting than the cutting line yet
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intersecting with a portion of said first cutting line so that a
waste portion is cut away from the semi-finished product at an
edge formed during said cutting out of the semi-finished product,
said cutting along the second cutting line being in a working
direction opposite to that of operation (A) so that an opposite
face of the workpiece is contacted first during said final cutting
than is contacted first during said cutting out of the first semi-
finished, wherein the rollover of the partial operation (A) is
filled up at least in the corner area where the first and second
cutting lines intersect.
[00130] In yet a further aspect the present invention resides
in a tool for fine blanking of a workpiece with relatively small
corner radii in relation to a thickness to be cut and reduced edge
reduction from a cutting strip, a sheet of a coil material or
other suitable starting material, comprising: a first tool part
and a second tool part between which the starting material is
clamped; each one of the first tool part and the second tool part
comprising at least one cutting die and at least one cutting
punch, the first tool part and the second tool part being
configured in a one-stage arrangement for cutting the workpiece
from the starting material; wherein the at least one cutting punch
of one of the first and second tool parts comprises a main punch
that cuts along a first cutting line a first vertical direction to
cut out from the starting material a first geometry of the
workpiece; wherein the at least one cutting punch of another of
the first and second tool parts comprises a second punch that cuts
in an opposite vertical direction from that of the main punch to
cut a refined geometry of the workpiece having said small corner
radii in relation to thickness; and wherein the second punch is
arranged with respect to the main punch in way that said second
punch can be applied to the first geometry to cut without applying
load in a same direction as the first punch, said second punch
cutting along a second cutting line different from and
intersecting the first cutting line, the arrangement and cutting
of the second punch relative to the main punch reducing edge
reduction at a portion of the fine blanked workpiece where said
second cutting line intersects said first cutting line.
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[0014] Further advantages and details accrue from the
following description with reference to the attached figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the following, the invention will be explained in more
detail with reference to the example of a preferred embodiment, and
wherein
[0016] Fig. 1 and 2 depict partially illustrated cross-section
of fine blanked parts according to the state of art of DE 39 31
320 Cl,
[0017] Fig. 3 a simplified schematic view of the tool
according to the invention during the execution of the first
partial step of the method according to the invention,
[0018] Fig. 4 depicts another simplified view of the method
according to the invention during the execution of the second
partial step of the method according to the invention,
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[0019] Fig. 5 shows the section of the cutting area
geometry of an interlocking part produced according to the
method of this invention as enlarged perspective view.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] With the method according to the invention, a workpiece
1 is fabricated, and in particular, an interlocking part of
greater thickness d, for instance 6.5 mm, by fine blanking the
interlocking part out of a cutting strip 2. The principle
layout of the fine blanking tool 3 corresponds to the known
state of the art. Thus a detailed description can be omitted.
For this reason, only the special features of the tool will be
emphasized in the following description.
[0021] The Fig. 1 and 2 show the cutting geometry of a fine
blanked and a counter fine blanked part 4 and 5, respectively
which is known from the state of the art according to DE 39 31
320 Cl. The fine blanked part 4 has an edge reduction 6, a
burnish 7 and a burr 8, wherein the burr 8 occurs on the side
opposite to the edge reduction 6. From the cutting geometry
of the counter fine blanked part 5, it can be seen that during
counter fine blanking, an edge reduction 9 occurs on both
sides. As a result, parts with sharp edges, as for example
interlocking parts, can not be fabricated with the necessary
dimensional accuracy.
[0022] As shown in Figures 3 to 5, the single-step fine
blanking tool 3 has a multi-step main punch 10. The strip
material 2 to be cut is clamped between a blank holder 11 and
a blanking die 12. The strip material 2 has a thickness d,
in this case 6.5 mm. In a first partial step A, the main
punch 10, the geometry of which respectively corresponds to
the interlocking part 1 to be fabricated, cuts a blank 13
(semi-finished product) in a vertical working direction. The
blank 13 is cut with a addendum circle 14 corresponding to a
subsequent toothing 15, out of the strip material 2. The
rollover 16 at the addendum circle 14 of blank 13 is
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negligibly small and lies on a side 17 of the blank 13, which
faces the applying main punch 10.
[0023] In a following partial step B (see Fig. 4) the
punches 18 (punches for cutting out the blanks between the
teeth) for the final cut of the interlocking part 1 are used.
The punches 18 are run back with the die plate 20, in the
opposite direction to partial step A, after moving a working
distance corresponding to the thickness d of the strip
material 2 to cut the teeth geometries 19 out of the blank
13, whereby the resulting waste portions 21 are also removed.
[0024] The corner portion of the rollover 16 from partial
step A is filled up again.
[0025] The cutting punch of the fine blanking tool 3 is
designed as a multi-part main punch 10 for cutting out a first
cutting geometry, for example, that of a blank 13. The
diameter of the blank 13 corresponds to the diameter of the
addendum circle of the toothing 15 of the interlocking part 1
to be fabricated. The working direction of the main punch 10
extends vertically. The main punch 10 is allocated at least
one punch 18 (punch for cutting out the blanks between the
teeth) for the final cut of the semi-finished product to
receive the interlocking part 1. The punch 18 works in the
opposite direction to the main punch 10 and with respect to
the first cutting geometry, the punch 18 is arranged in a way
that it can be applied to it without applying the pressure
load in the same direction.
[0026] In the case of fabrication of an interlocking part
1, the cutting geometry of the main punch 10 is an addendum
circle. But it also can be a geometry consisting of a complex
contour of steady or unsteady curves, if other parts with
other complex shapes are to be fine blanked.
[0027] The punches 18 for the final cut advantageously have
geometries of a contour with steady or unsteady curves.
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[0028] Thereby the cutting geometries of the main punch 10
and punch 18 can be varied, so that complex parts can be
composed of simple geometries, respectively.
[0029] The fine blanking tool 3 has a single-step structure.
It facilitates contradirectional and directly adjoining cutting
operations described above as partial steps A and B.
[0030] Thus the converging tool geometries of main punch 10
and punch 18 for cutting out the blanks between the teeth are
not subjected to pressure load at the same time, nor in the
same direction. As a result, the otherwise necessary corner
radius to reduce the partial compression tensions in the tip
portions of the interlocking part can be avoided.
Fig. 5 shows as an example an interlocking part fabricated
according to the method of the invention.
[0031] Thus it is possible to produce complex workpieces or
parts of greater thickness with sharp edges and significantly
reduced rollover in a economically efficient way by fine
blanking.
[0032] List of reference signs
Interlocking part, 1
Strip material 2
Fine blanking tool 3
Cross section of a part produced by fine
blanking according to the state of the art 4
Cross section of a part produced by counter
fine blanking according to the state of the art 5
Edge reduction 6
Burnish 7
Burr 8
Rollover on both sides 9
Main punch 10
Blank holder 11
Cutting die 12
Blank (semi-finished product) 13
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Addendum circle of 15 14
Toothing 15
Rollover of 13 16
Side of 13 17
Punch (for cutting out blanks between teeth) 18
Tooth geometry 19
Die-plate 20
Waste portion 21
Thickness of 2 d
Partial step A
Partial step B
